how do I use my iPad Pro as a second screen?
How do I use my iPad Pro as a second screen to my MacBook Pro?
iPad Pro, iPadOS 14
An iPad Pro can be used with a compatible Mac to extend the Mac display to the iPad using the Catalina/iPadOS Sidecar feature.
https://support.apple.com/en-gb/HT210380#systemrequirements
An alternative third-party product, Duet, can be used to extend a PC or Mac to an iPad:
